Helicobacter pylori infects the stomach of half of the world's population. This infection is a primary cause of peptic ulcer disease and a high risk factor for gastric cancer. Therefore, eradication of this H. pylori infection leads to ulcer healing and lowers the risk of gastric cancer. Until the discovery of H. pylori, it was thought that stomach acid presented an inhospitable environment for bacterial infection. However, H. pylori has uniquely developed the means of surviving and growing on the acidic surface of the human stomach, a process termed acid acclimation. Disruption of this process leads to loss of survival in acid, therefore the components of this process would provide novel targets for eradication therapy. Current eradication therapies require the use of antibiotics along with acid inhibitory drugs. The successful eradication by these therapies is decreasing due to increasing antibiotic resistance, resulting in a response rate of < 80% in the USA. Acid acclimation is the ability of the organism to maintain a neutral periplasmic pH homeostasis in the presence of acid to allow gastric infection. Bacteria sense and respond to environmental stimuli via two component histidine kinase signaling systems. In the case of H. pylori, environmental acidification sensing is initiated through the HP0165/HP0166 two component system. Accordingly, the first hypothesis to be explored is that graded responses to acidity are regulated by this HP0165/HP0166 two component system. The system responds by acid-induced transcriptional upregulation of two promoters in the urease gene cluster, pureA and pureI, acid-induced post-translational upregulation of assembly UreI with apourease and the urease accessory proteins required for Ni2+ insertion along with Ni2+ entry, and also post-transcriptional down regulation by sRNAs at neutral pH. The UreI/urease membrane assembly is essential for acid acclimation and acid survival of the organism, and an understanding of the assembly mechanism is required for targeted therapy to this process. Therefore, the role of the HP0165/HP0166 TCS in membrane recruitment, assembly and activation of urease, in regulation of sRNA control of urease expression, and pH sensing by the TCS will be explored. The growth dependent antibiotics clarithromycin or amoxicillin are not effective unless bacteria are in growth phase. Improving acid inhibition should improve therapeutic outcome. In the second aim, we hypothesize that inhibition of acid secretion increases the number of bacteria in growth phase, making them sensitive to growth dependent antibiotics necessitating the requirement for administration of acid inhibitory compounds, in addition to antibiotics for successful eradication. The finding that slow omeprazole metabolizers respond with much improved acid control and effective eradication with omeprazole and amoxicillin alone, suggests that improved acid inhibition increases the sensitivity of the organism to growth dependent antibiotics. From this it follows that, with more consistent and greater elevation of intragastric pH, more organisms are in the antibiotic sensitive growth phase rather than the resistant stationary phase. Maintenance of an elevated pH for both day and night should put almost all H. pylori in growth phase. Therefore, the effect of acid inhibition on the rate of H. pylori protein synthesis as an indicator of bacterial cell growth will be measured in vitro and in vivo. PUBLIC HEALTH RELEVANCE: H. pylori infection has a causal role in peptic ulcer disease and increases the risk of gastric cancer. Peptic ulcer disease and gastric cancer are major causes of morbidity in the Veterans population, in the United States and worldwide. H. pylori inhabits the stomach and has evolved unique acid response mechanisms to allow gastric colonization. Standard triple or quadruple therapies with acid blocking medicines and antibiotics have become less effective, falling below 80% success rate due to increasing antibiotic resistance. An understanding of how H. pylori colonizes the stomach will aid the development of novel eradication therapies. A possible strategy to replace current therapy is to target genes that allow the bacteria to survive in acid with non-antibiotic compounds. Another possible strategy is to improve control of the pH of the bacterial environment, so that dual therapy with acid inhibition and amoxicillin could be used. This would involve development of drugs with better acid blocking properties.